Implantable spiral wound stimulation electrodes

ABSTRACT

Electrical stimulation electrodes for implantation within a living body for transmission of stimuli to excitable neural or contractile cells. The electrodes are characterized by flexibility to permit following of contour variations and maintenance of electrical contact with the stimulation region. The electrodes include a pair of parallel spaced apart helically wound conductors maintained in this configuration. When the electrode is implanted, undesired excitation of nearby structures can be avoided.

United States Patent 1 1 Timm et al.

[451 Sept. 25, 1973 1 1 IMPLANTABLE SPIRAL WOUND STIMULATION ELECTRODES[75] Inventors: Gerald W. Timm; William E.

Bradley, both of Minneapolis, Minn.

[73] Assignee: The Regents of the University of Minnesota, Minneapolis,Minn.

[22] Filed: Mar. 19, 1971 [21] Appl. No.: 126,145

[52] US. Cl. 128/418, 128/419 E, 174/113 C, 174/130 [51] Int. Cl A61111/04 [58] Field of Search 128/404, 416, 418, 128/419 E; 174/113 C, 130

{56] References Cited UNITED STATES PATENTS 3,474,791 10/1969 Bentov128/418 3,453,374 7/1969 Natwick 174/113 C 3,035,583 5/1962 Hirsch etal. 128/418 3,572,344 3/1971 Bolduc .1 128/418 Primary Examiner-WilliamE. Kamm Attorney-Burd, Braddock & Bartz [57] ABSTRACT Electricalstimulation electrodes for implantation within a living body fortransmission of stimuli to excitable neural or contractile cells. Theelectrodes are characterized by flexibility to permit following ofcontour variations and maintenance of electrical contact with thestimulation region. The electrodes include a pair of parallel spacedapart helically wound conductors maintained in this configuration. Whenthe electrode is implanted, undesired excitation of nearby structurescan be avoided.

10 Claims, 5 Drawing lFigures IMPLANTABLE SPIRAL WOUND STIMULATIONELECTRODES The invention described herein was made in the course of workunder a grant or award from the Department of Health, Education andWelfare.

This invention relates to implantable stimulation electrodes for theapplication in a living body of a current of sufficient magnitude inproximity of any desired excitable neural or contractile cells toactivate those neural or contractile cells in the immediate vicinity ofthe electrode while avoiding excitation of nearby structures. Althoughnot limited thereto, the electrodes are useful in bladder stimulationsystems, of which those disclosed in the patents of co-inventor WilliamE.

Bradley, US. Pat. No. 3,236,240 and No. 3,543,761,

are exemplary.

Previous stimulation electrodes have included single or concentric discelectrodes which are characterized by a lack of mechanical flexibilitywhich often causes them to lose electrical contact with the stimulationregion. Grid or mesh electrodes have electrical characteristics whichrequire the use of a backing sheet of insulative material which causethe electrode to give unidirectional stimulation. Such electrodes havethe further disadvantage that any large sheet covering a contractileorgan in the body causes a massive fibrotic reaction that ultimatelyimpairs the organs contractile ability. Prior art electrodes have hadthe further disadvantage of induction of wide current fields whichstimulate contiguous structures in an undesirable manner.

The electrode according to the present invention is flexible such thatit can follow contour variations in an organ without interfering withthe organs normal contractile function. The electrode may be embedded inthe wall of the organ so that'only neural and contractile cells locatedwithin this wall will be excited when electrical stimuli are appliedfTheelectrode is characterized by two parallel conducting wires extending ina helical fashion and maintained in this configuration.

The invention is illustrated in the accompanying drawings in which:

FIG. 1 is a diagrammatic illustration of one form of spiral woundelectrode with insulating core material;

FIG. 2 is a similardiagrammatic illustration showing the approximatevolume of tissue which is stimulated by a stimulus applied in the use ofthe electrode;

FIGS. 3 and 4 are diagrammatic illustrations of the steps of animbrication technique for embedding the electrode in tissue to beelectrically stimulated; and

FIG. 5 is an illustration of an alternative form of electrode inwhichconductor wires are interwoven with insulative spacing andsupporting strands.

Referring to FIG. 1, the electrode, indicated generally at 10, iscomprised of two parallel conducting wires 11 and 12 wrapped helicallyaround a flexible cylindrical insulative core 13. Current flow betweenconductors l1 and 12 is provided through the tissue in which theelectrodes are embedded. The lead-in conductors 15 and 16 are insulatedby flexible insulative tubes 17 and 18, respectively, between the sourceof electrical stimuli and the body situs to be stimulated by theelectrode. By using a small diameter core, between about 1 to 3millimeters, and varying the spacing between the two wires, the fieldconfining properties of the electrode can be varied.

' The spatial relationship between conductors 11 and 12 may bemaintained by providing core 13 with shallow spiral channels or groovesin which the conductors are wound; or the conductors may be secured bymeans of adhesive material, such as medical grade Silastic adhesive; orthe conductor may be produced by printed circuit techniques.

The flexibility of the electrode configuration is determined by themechanical properties of the core and of the wires. The wire can be anyimplantable electrical current conductor, such as stainless steel,platinum or one of its alloys, such as platinum-irridium, carbonimpregnated polyester (Dacron), or the like. The insulating core istypically made from implantable grade silicone rubber, nylon, silk, orother implantable insulating material. The insulating tubes 17 and 18for the lead-in wires are typically implantable silastic orpolytetrafluoroethylene (Teflon) tubing.

As seen in broken lines in FIG. 2, experimentation has shown thatstimulus is effective within a volume described by a cylinder 20concentric to the electrode 10, the diameter of the cylinder being equalto the diameter D of the electrode plus twice the spacing 5 between thehelical wires (D 28) and with a height or length equal to the electrodelength L plus the cylinder diameter (L D 25). As a general rule, thebest confining properties of the electrode are achieved when the spacingS between parallel wires 11 and 12 approximately equals the diameter Dof the electrode. For example, to stimulate the nerve net supplying theintestine or urinary bladder, the electrodes were made with the spacingbetween the conductors and diameter equal, and between about I and 3millimeters. Stimuli were completely confined to the intestinal orbladder wall during chronic implants of two months duration. The tissueremained excitable during this time when stimulated at rates between 10and 40 pulses per second at pulse amplitudes below 50 volts.Intravesical pressure rises in excess of centimeters H O were typicallyobtained and complete bladder evacuation was induced.

The electrode is so designed that it will follow contour variations inan organ stimulated by it without interfering with the organs normalcontractile function. Thus, by embedding the electrode in the wall of anorgan, only neural and contractile cells located within this wall willbe excited when electrical stimuli are applied between the two wires inthe electrode so that contraction of only the stimulated organ will beaccomplished. The electrode can be surgically embedded by incision ofthe outer layers of the organ to be stimulated, placing the electrodeentirely in the wound produced by the incision and suturing over it.

1 Alternatively, as shown in FIGS. 3 and 4, the electrode 10 may bepositioned on the surface 21 of the organ by means of sutures 22. Thesutures 22 are passed into and out of the tissue 23 of the organ on oneside of the electrode, passed over the electrode and then into and outof the tissue on the opposite side, as

' shown in FIG. 3. Then, as shown in FIG. 4, the elecstrands such asbraided nylon suture, silk, polyester, or the like. Conductors 11A and12A are wrapped helically in parallel spaced relation, with the spacingbetween conductors approximately equaling the diameter of the electrode,as already described. In order to maintain the conductors spaced fromone another, a pair of insulator spacer strands 25 and 26 are wrapped inthe same helical fashion spaced between the adjacent winds of theconductors. These insulative strands 25 and 26 are shown as beingstippled, for greater clarity.

The conductor wires 11A and 11B and alternating spacers 25 and 26 aremaintained in the described relationship by means of four insulativestrands 27-30 helically wound in the opposite direction from theconductor and spacer strands with substantially the same spacing andinterwoven with the conductors and spacers. Thus it will be seen thatone supporting strand is interwoven so as to pass under each conductorwire and over each spacer strand. The next adjacent supporting strand isinterwoven to pass over each conductor wire and under each spacer strandand so on for the length of the electrode. The result is a symmetricaltubular configuration in which the helical spatial relationship of theconductor wires is maintained and separation of the wires is assured. Aflexible insulative core may be within the electrode or not, as desired.For convenience the woven electrode is shown as formed on an elongatedcylindrical core or mandrel which may be removed before the electrode isput into use. Conductors are provided with insulated lead-ins forconnection to a source of electrical stimuli. This form of electrode maybe imbricated in the manner already described.

It is apparent that many modifications and variations of this inventionas hereinbefore set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only and the invention is limited only by the terms of theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An electrical stimulation electrode for implantation in a livingbody, said electrode consisting essentially of:

A. a pair of elongated parallel spaced apart helically wound electricalconductors, said conductors being conductive filaments,

B. means for supporting and maintaining said conductors in parallelspaced apart helically wound configuration, said means comprising:

1. a pair of elongated parallel spaced apart helically wound insulativespacer strands, said spacer strands being alternated with saidconductors and wound in the same direction, and

2. two pairs of elongated parallel spaced apart helically woundinsulative supporting strands, said supporting strands being wound inthe opposite direction from said conductors and spacer strands andinterwoven therewith, and

C. insulated conductor means for connecting said helically woundconductors to a source of electrical stimuli.

2. An electrical stimulation electrode according to claim 1 furthercharacterized in that said conductors are spaced apart a distance aboutequal to the diameter of the helical configuration.

3. An electrical stimulation electrode according to claim 2 furthercharacterized in that the spacing between said conductors and thediameter of said helaical configuration are between about 1 and 3 mm.

4. An electrical stimulation electrode according to claim 1 furthercharacterized in that said insulative strands are formed from nylon.

5. An electrical stimulation electrode according to claim 1 furthercharacterized in that said insulative strands are formed from silk.

6. An electrical stimulation electrode according to claim 1 furthercharacterized in that said insulative strands are formed from polyester.

7. An electrical stimulation electrode according to claim 1 furthercharacterized in that said conductors are formed from stainless steelwire.

8. An electrical stimulation electrode according to claim 1 furthercharacterized in that said conductors are formed from platinum wire.

9. An electrical stimulation electrode according to claim 1 furthercharacterized in that said conductors are formed from platinum alloywire.

10. An electrical stimulation electrode according to claim 1 furthercharacterized in that said conductors are formed from carbon impregnatedpolyester filament.

1. An electrical stimulation electrode for implantation in a livingbody, said electrode consisting essentially of: A. a pair of elongatedparallel spaced apart helically wound electrical conductors, saidconductors being conductive filaments, B. means for supporting andmaintaining said conductors in parallel spaced apart helically woundconfiguration, said means comprising:
 1. a pair of elongated parallelspaced apart helically wound insulative spacer strands, said spacerstrands being alternated with said conductors and wound in the samedirection, and
 2. two pairs of elongated parallel spaced apart helicallywound insulative supporting strands, said supporting strands being woundin the opposite direction from said conductors and spacer strands andinterwoven therewith, and C. insulated conductor means for connectingsaid helically wound conductors to a source of electrical stimuli. 2.two pairs of elongated parallel spaced apart helically wound insulativesupporting strands, said supporting strands being wound in the oppositedirection from said conductors and spacer strands and interwoventherewith, and C. insulated conductor means for connecting saidhelically wound conductors to a source of electrical stimuli.
 2. Anelectrical stimulation electrode according to claim 1 furthercharacterized in that said conductors are spaced apart a distance aboutequal to the diameter of the helical configuration.
 3. An electricalstimulation electrode according to claim 2 further characterized in thatthe spacing between said conductors and the diameter of said helaicalconfiguration are between about 1 and 3 mm.
 4. An electrical stimulationelectrode according to claim 1 further characterized in that saidinsulative strands are formed from nylon.
 5. An electrical stimulationelectrode according to claim 1 further characterized in that saidinsulative strands are formed from silk.
 6. An electrical stimulationelectrode according to claim 1 further characterized in that saidinsulative strands are formed from polyester.
 7. An electricalstimulation electrode according to claim 1 further characterized in thatsaid conductors are formed from stainless steel wire.
 8. An electricalstimulation electrode according to claim 1 further characterized in thatsaid conductors are formed from platinum wire.
 9. An electricalstimulation electrode according to claim 1 further characterized in thatsaid conductors are formed from platinum alloy wire.
 10. An electricalstimulation electrode according to claim 1 further characterized in thatsaid conductors are formed from carbon impregnated polyester filament.